1. Field of the Invention
The present invention relates to a camshaft supporting structure in an engine for supporting a camshaft having a plurality of valve operating cams and a plurality of journal portions on intermediate bearing portions formed in a cylinder head.
2. Description of the Prior Art
When a camshaft is supported in a cam chamber provided in a cylinder head of an engine, if the camshaft has a short overall length, such as a camshaft for a single-cylinder engine or a 2-cylinder engine, opposite ends of the camshaft can be supported in a sidewall of a cylinder head. When a camshaft has a long overall length, however, if opposite ends thereof are only supported, such as a camshaft of a large-size engine such as a 3- or more-cylinder engine, the camshaft may be flexed. For this reason, a journal portion formed at an intermediate portion of the camshaft is supported on an intermediate bearing means provided in the cylinder head.
The intermediate bearing means comprises an intermediate bearing boss integrally formed in the cylinder head and a bearing cap coupled to the intermediate bearing boss by a bolt, so that the journal portion of the camshaft is clamped between the intermediate bearing boss and the bearing cap, or comprises a bearing hole defined in an intermediate bearing boss integrally formed on the cylinder head, so that the journal portion may be fitted into the bearing hole.
In the former case, the bearing cap and the bolt are required, resulting in an increased number of components, but in the latter case, the bearing cap and the bolt are not required, resulting in a decreased number of components. In the latter case, however, the following problem is encountered: in inserting the camshaft into the bearing hole in the intermediate bearing boss, the valve operating cam interferes with the bearing hole having a diameter smaller than the largest diameter of the valve operating cam. For this reason, a notch for permitting the valve operating cam to pass therethrough must be formed in the bearing hole, and the camshaft must be inserted while being rotated to align the phase of the valve operating cam with the phase of the notch, resulting in a slow assembly rate.